This work, which uses Neurospora as an experimental organism, is guided by the working hypothesis that localized increases in the level of calcium in the hyphal cytosol constitute signals for wall extension, and hence for the formation and maintenance of growing apices. During this coming year we shall continue to test the above working hypothesis as indicated on the previous Notice of Research Project, and will also focus on the contrasting roles of calcium and cAMP in Neurospora. Contrasting effects have been reported for branching, can be paralleled in vitro by the activation of phosphodiesterase by calmodulin, and are also in evidence in studies where permeabilized Neurospora is allowed to autolyze its wall after labeling it with radioactive N-acetylglucosamine.